contribs/JimMoore/LoggingOutputStream.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


import java.io.*;
import org.apache.log4j.*;


/**
 * An OutputStream that flushes out to a Category.<p>
 * 
 * Note that no data is written out to the Category until the stream is
 *   flushed or closed.<p>
 * 
 * Example:<pre>
 * // make sure everything sent to System.err is logged
 * System.setErr(new PrintStream(new LoggingOutputStream(Category.getRoot(), Priority.WARN), true));
 * 
 * // make sure everything sent to System.out is also logged
 * System.setOut(new PrintStream(new LoggingOutputStream(Category.getRoot(), Priority.INFO), true));
 * </pre>
 * 
 * @author <a href="mailto://Jim.Moore@rocketmail.com">Jim Moore</a>
 * @see Category
 */
public class LoggingOutputStream extends OutputStream {
  protected static final String LINE_SEPERATOR = System.getProperty("line.separator");


  /**
   * Used to maintain the contract of {@link #close()}.
   */
  protected boolean hasBeenClosed = false;

  /**
   * The internal buffer where data is stored. 
   */
  protected byte[] buf;

  /**
   * The number of valid bytes in the buffer. This value is always 
   *   in the range <tt>0</tt> through <tt>buf.length</tt>; elements 
   *   <tt>buf[0]</tt> through <tt>buf[count-1]</tt> contain valid 
   *   byte data.
   */
  protected int count;


  /**
   * Remembers the size of the buffer for speed.
   */
  private int bufLength;

  /**
   * The default number of bytes in the buffer. =2048
   */
  public static final int DEFAULT_BUFFER_LENGTH = 2048;


  /**
   * The category to write to.
   */
  protected Category category;

  /**
   * The priority to use when writing to the Category.
   */
  protected Priority priority;


  private LoggingOutputStream() {
    // illegal
  }


  /**
   * Creates the LoggingOutputStream to flush to the given Category.
   * 
   * @param cat        the Category to write to
   * 
   * @param priority   the Priority to use when writing to the Category
   * 
   * @exception IllegalArgumentException
   *                   if cat == null or priority == null
   */
  public LoggingOutputStream(Category cat, Priority priority)
  throws IllegalArgumentException {
    if (cat == null) {
      throw new IllegalArgumentException("cat == null");
    }
    if (priority == null) {
      throw new IllegalArgumentException("priority == null");
    }

    this.priority = priority;
    category = cat;
    bufLength = DEFAULT_BUFFER_LENGTH;
    buf = new byte[DEFAULT_BUFFER_LENGTH];
    count = 0;
  }


  /**
   * Closes this output stream and releases any system resources
   *   associated with this stream. The general contract of <code>close</code>
   *   is that it closes the output stream. A closed stream cannot perform
   *   output operations and cannot be reopened.
   */
  public void close() {
    flush();
    hasBeenClosed = true;
  }


  /**
   * Writes the specified byte to this output stream. The general
   * contract for <code>write</code> is that one byte is written
   * to the output stream. The byte to be written is the eight
   * low-order bits of the argument <code>b</code>. The 24
   * high-order bits of <code>b</code> are ignored.
   * 
   * @param b          the <code>byte</code> to write
   * 
   * @exception IOException
   *                   if an I/O error occurs. In particular,
   *                   an <code>IOException</code> may be thrown if the
   *                   output stream has been closed.
   */
  public void write(final int b) throws IOException {
    if (hasBeenClosed) {
      throw new IOException("The stream has been closed.");
    }

    // don't log nulls
    if (b == 0) {
      return;
    }

    // would this be writing past the buffer?
    if (count == bufLength) {
      // grow the buffer
      final int newBufLength = bufLength+DEFAULT_BUFFER_LENGTH;
      final byte[] newBuf = new byte[newBufLength];

      System.arraycopy(buf, 0, newBuf, 0, bufLength);

      buf = newBuf;
      bufLength = newBufLength;
    }

    buf[count] = (byte)b;
    count++;
  }


  /**
   * Flushes this output stream and forces any buffered output bytes
   *   to be written out. The general contract of <code>flush</code> is
   *   that calling it is an indication that, if any bytes previously
   *   written have been buffered by the implementation of the output
   *   stream, such bytes should immediately be written to their
   *   intended destination.
   */
  public void flush() {
    if (count == 0) {
      return;
    }

    // don't print out blank lines; flushing from PrintStream puts out these
    if (count == LINE_SEPERATOR.length()) {
      if ( ((char)buf[0]) == LINE_SEPERATOR.charAt(0)  &&
           ( ( count == 1 ) ||  // <- Unix & Mac, -> Windows
             ( (count == 2) && ((char)buf[1]) == LINE_SEPERATOR.charAt(1) ) ) ) {
        reset();
        return;
      }
    }

    final byte[] theBytes = new byte[count];

    System.arraycopy(buf, 0, theBytes, 0, count);

    category.log(priority, new String(theBytes));

    reset();
  }


  private void reset() {
    // not resetting the buffer -- assuming that if it grew that it
    //   will likely grow similarly again
    count = 0;
  }

}